Terrestrial wireless positioning in licensed and unlicensed frequency bands

ABSTRACT

Disclosed are techniques for determining a distance (or range) between a first wireless entity and a second wireless entity. In an aspect, the first wireless entity transmits a first positioning reference signaling (PRS) signal to the second wireless entity at a first time, where the first PRS signal is received by the second wireless entity at a second time, and receives a second PRS signal from the second wireless entity at a third time, where the second PRS signal is transmitted by the second wireless entity at a fourth time. The first wireless entity enables the distance to be determined by a location computing entity, for example, by a location server, based on the first, second, third, and fourth times. The first wireless entity may be a mobile device or a base station and the second wireless entity may be the other of the mobile device or base station.

CROSS-REFERENCE TO RELATED APPLICATIONS FOR PATENT

The present application for patent is a continuation of U.S. patentapplication Ser. No. 16/586,766, entitled “TERRESTRIAL WIRELESSPOSITIONING IN LICENSED AND UNLICENSED FREQUENCY BANDS,” filed Sep. 27,2019, which is a continuation of U.S. patent application Ser. No.15/607,409, entitled “TERRESTRIAL WIRELESS POSITIONING IN LICENSED ANDUNLICENSED FREQUENCY BANDS,” filed May 26, 2017, each of which isassigned to the assignee hereof, and expressly incorporated herein byreference in its entirety.

BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure

Aspects of the disclosure relate to positioning of a user equipment (UE)that has access to a terrestrial wireless network using a licensed orunlicensed frequency band.

2. Description of the Related Art

Wireless communication systems are widely deployed to provide varioustypes of communication content, such as voice, data, multimedia, and soon. Typical wireless communication systems are multiple-access systemscapable of supporting communication with multiple users by sharingavailable system resources (e.g., bandwidth, transmit power, etc.).Examples of such multiple-access systems include Code Division MultipleAccess (CDMA) systems, Time Division Multiple Access (TDMA) systems,Frequency Division Multiple Access (FDMA) systems, Orthogonal FrequencyDivision Multiple Access (OFDMA) systems, and others. These systems areoften deployed in conformity with specifications such as Long TermEvolution (LTE) provided by the Third Generation Partnership Project(3GPP), Ultra Mobile Broadband (UMB) and Evolution Data Optimized(EV-DO) provided by the Third Generation Partnership Project 2 (3GPP2),802.11 provided by the Institute of Electrical and Electronics Engineers(IEEE), etc.

In cellular networks, “macro cell” access points provide connectivityand coverage to a large number of users over a certain geographicalarea. A macro network deployment is carefully planned, designed, andimplemented to offer good coverage over the geographical region. Toimprove indoor or other specific geographic coverage, such as forresidential homes and office buildings, additional “small cell,”typically low-power access points have recently begun to be deployed tosupplement conventional macro networks. Small cell access points mayalso provide incremental capacity growth, richer user experience, and soon.

Small cell LTE operations, for example, have been extended into theunlicensed frequency spectrum such as the Unlicensed NationalInformation Infrastructure (U-NII) band used by Wireless Local AreaNetwork (WLAN) technologies. This extension of small cell LTE operationis designed to increase spectral efficiency and hence capacity of theLTE system.

Positioning of a UE with access to a wireless network employing licensedor unlicensed spectrum (e.g., an LTE network using licensed spectrum oran LTE Unlicensed (LTE-U) network) may be beneficial or even critical tosupport certain applications, such as emergency calls, personalnavigation, direction finding, person finding, asset tracking, etc.However, current state of art positioning may have limited accuracyand/or excessive response time in certain environments (e.g., indoors)and/or using certain types of networks (e.g., private LTE-U networks).Improvements in positioning support for such environments and/ornetworks may be desirable.

SUMMARY

The following presents a simplified summary relating to one or moreaspects disclosed herein. As such, the following summary should not beconsidered an extensive overview relating to all contemplated aspects,nor should the following summary be regarded to identify key or criticalelements relating to all contemplated aspects or to delineate the scopeassociated with any particular aspect. Accordingly, the followingsummary has the sole purpose to present certain concepts relating to oneor more aspects relating to the mechanisms disclosed herein in asimplified form to precede the detailed description presented below.

In an aspect, a method at a first wireless entity for determining adistance to a second wireless entity includes transmitting a firstpositioning reference signaling (PRS) signal to the second wirelessentity at a first time, wherein the first PRS signal is received by thesecond wireless entity at a second time, receiving a second PRS signalfrom the second wireless entity at a third time, wherein the second PRSsignal is transmitted by the second wireless entity at a fourth time,and enabling the distance to be determined by a location computingentity based on the first time, the second time, the third time, and thefourth time.

In an aspect, an apparatus for determining a distance from a firstwireless entity to a second wireless entity includes a transceiver ofthe first wireless entity configured to: transmit a first PRS signal tothe second wireless entity at a first time, wherein the first PRS signalis received by the second wireless entity at a second time, and receivea second PRS signal from the second wireless entity at a third time,wherein the second PRS signal is transmitted by the second wirelessentity at a fourth time, and at least one processor of the firstwireless entity configured to: enable the distance to be determined by alocation computing entity based on the first time, the second time, thethird time, and the fourth time.

In an aspect, a non-transitory computer-readable medium storingcomputer-executable instructions for determining a distance from a firstwireless entity to a second wireless entity includes computer-executableinstructions comprising at least one instruction to cause the firstwireless entity to transmit a first PRS signal to the second wirelessentity at a first time, wherein the first PRS signal is received by thesecond wireless entity at a second time, at least one instruction tocause the first wireless entity to receive a second PRS signal from thesecond wireless entity at a third time, wherein the second PRS signal istransmitted by the second wireless entity at a fourth time, and at leastone instruction to cause the first wireless entity to enable thedistance to be determined by a location computing entity based on thefirst time, the second time, the third time, and the fourth time.

In an aspect, an apparatus for determining a distance from a firstwireless entity to a second wireless entity includes a communicationmeans of the first wireless entity configured to: transmit a first PRSsignal to the second wireless entity at a first time, wherein the firstPRS signal is received by the second wireless entity at a second time,and receive a second PRS signal from the second wireless entity at athird time, wherein the second PRS signal is transmitted by the secondwireless entity at a fourth time, and a processing means of the firstwireless entity configured to: enable the distance to be determined by alocation computing entity based on the first time, the second time, thethird time, and the fourth time.

Other objects and advantages associated with the aspects disclosedherein will be apparent to those skilled in the art based on theaccompanying drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are presented to aid in the description ofvarious aspects of the disclosure and are provided solely forillustration of the aspects and not limitation thereof.

FIG. 1 illustrates a high-level system architecture of a wirelesscommunications system in accordance with an aspect of the disclosure.

FIG. 2 illustrates an example configuration of radio access networks(RANs) and a packet-switched portion of a core network that is based onan LTE network in accordance with an aspect of the disclosure.

FIG. 3 is a simplified block diagram of several sample aspects ofcomponents that may be employed in wireless communication nodes andconfigured to support communication as taught herein.

FIG. 4A illustrates an example of determining a propagation time betweenan eNodeB and a UE.

FIG. 4B illustrates another example of determining a propagation timebetween an eNodeB and a UE.

FIG. 5 illustrates an example of a technique for positioning of a UE inthe wireless communication system of FIG. 1.

FIG. 6 illustrates an exemplary flow for determining a distance betweena first wireless entity and a second wireless entity according to atleast one aspect of the disclosure.

FIG. 7 illustrates an exemplary flow for positioning a UE according toat least one aspect of the disclosure.

FIGS. 8 and 9 are other simplified block diagrams of several sampleaspects of apparatuses configured to support positioning andcommunication as taught herein.

Elements, stages, steps, and/or actions with the same reference label indifferent drawings may correspond to one another (e.g., may be similaror identical to one another). Further, some elements in the variousdrawings are labelled using a numeric prefix followed by an alphabeticor numeric suffix. Elements with the same numeric prefix but differentsuffixes may be different instances of the same type of element. Thenumeric prefix without any suffix is used herein to reference anyelement with this numeric prefix. For example, different instances102-1, 102-2, 102-3, 102-4, 102-5, and 102-N of a UE are shown inFIG. 1. A reference to a UE 102 then refers to any of UEs 102-1, 102-2,102-3, 102-4, 102-5, and 102-N. Likewise, in FIG. 1, any reference to alocation server 170 can refer to either location server 170A or locationserver 170B in FIG. 1.

DETAILED DESCRIPTION

Disclosed are techniques for determining a distance (or range) between apair of wireless entities (e.g., a UE and eNodeB). Also disclosed aretechniques for positioning of a UE at a location server based onmeasurements of signal propagation time and timing differences betweensignals received at the UE from two or more pairs of base stations.

These techniques and other aspects are disclosed in the followingdescription and related drawings directed to specific aspects of thedisclosure. Alternate aspects may be devised without departing from thescope of the disclosure. Additionally, well-known elements of thedisclosure will not be described in detail or will be omitted so as notto obscure the relevant details of the disclosure.

The words “exemplary” and/or “example” are used herein to mean “servingas an example, instance, or illustration.” Any aspect described hereinas “exemplary” and/or “example” is not necessarily to be construed aspreferred or advantageous over other aspects. Likewise, the term“aspects of the disclosure” does not require that all aspects of thedisclosure include the discussed feature, advantage or mode ofoperation.

Further, many aspects are described in terms of sequences of actions tobe performed by, for example, elements of a computing device. It will berecognized that various actions described herein can be performed byspecific circuits (e.g., application specific integrated circuits(ASICs)), by program instructions being executed by one or moreprocessors, or by a combination of both. Additionally, these sequence ofactions described herein can be considered to be embodied entirelywithin any form of non-transitory computer-readable storage mediumhaving stored therein a corresponding set of computer instructions that,upon execution, would cause or instruct an associated processor of adevice to perform the functionality described herein, such as thefunctionality described with reference to FIGS. 6 and 7. Thus, thevarious aspects of the disclosure may be embodied in a number ofdifferent forms, all of which have been contemplated to be within thescope of the claimed subject matter. In addition, for each of theaspects described herein, the corresponding form of any such aspects maybe described herein as, for example, “logic configured to” perform thedescribed action.

A mobile device, also referred to herein as a UE, may be mobile or may(e.g., at certain times) be stationary, and may communicate with a radioaccess network (RAN). As used herein, the term “UE” may be referred tointerchangeably as an “access terminal” or “AT,” a “client device,” a“wireless device,” a “subscriber device,” a “subscriber terminal,” a“subscriber station,” a “user terminal” or UT, a “mobile terminal,” a“mobile station,” or variations thereof. Generally, UEs can communicatewith a core network via a RAN, and through the core network the UEs canbe connected with external networks such as the Internet and with otherUEs. Of course, other mechanisms of connecting to the core networkand/or the Internet are also possible for the UEs, such as over wiredaccess networks, WiFi networks (e.g., based on IEEE 802.11, etc.) and soon. UEs can be embodied by any of a number of types of devices includingbut not limited to printed circuit (PC) cards, compact flash devices,external or internal modems, wireless or wireline phones, smartphones,tablets, tracking devices, asset tags, and so on. A communication linkthrough which UEs can send signals to a RAN is called an uplink channel(e.g., a reverse traffic channel, a reverse control channel, an accesschannel, etc.). A communication link through which the RAN can sendsignals to UEs is called a downlink or forward link channel (e.g., apaging channel, a control channel, a broadcast channel, a forwardtraffic channel, etc.). As used herein the term traffic channel (TCH)can refer to either an uplink/reverse or downlink/forward trafficchannel.

FIG. 1 illustrates a high-level system architecture of a wirelesscommunications system 100 in accordance with an aspect of thedisclosure. The wireless communications system 100 contains UEs 1 to N(referenced as 102-1 to 102-N). The UEs 102-1 to 102-N can includecellular telephones, personal digital assistant (PDAs), pagers, a laptopcomputer, a tablet computer, a desktop computer, and so on. For example,in FIG. 1, UE 102-1 and UE 102-2 are illustrated as cellular featurephones, UEs 102-3, 102-4, and 102-5 are illustrated as cellulartouchscreen phones, or “smartphones,” and UE 102-N is illustrated as adesktop computer, or personal computer (often referred to as a “PC”).Although only six UEs 102 are shown in FIG. 1, the number of UEs 102 inwireless communications system 100 may be in the hundreds, thousands, ormillions (e.g., N may be any number up to or greater than one million).

Referring to FIG. 1, UEs 102-1 to 102-N are configured to communicatewith one or more access networks (e.g., the RANs 120A and 120B, theaccess point 125, etc.) over a physical communications interface orlayer, shown in FIG. 1 as air interfaces 104, 106, and 108 and/or adirect wired connection. The air interfaces 104 and 106 can comply witha given cellular communications protocol (e.g., Code Division MultipleAccess (CDMA), Evolution-Data Optimized (E-VDO), Enhanced High RatePacket Data (eHRPD), Global System for Mobile communications (GSM),Wideband CDMA (W-CDMA), LTE, LTE-U, etc.), while the air interface 108can comply with a Wireless Local Area Network (WLAN) protocol (e.g.,IEEE 802.11). Both RAN 120A and 120B may include a plurality of accesspoints that serve UEs over air interfaces, such as the air interfaces104 and 106. The access points in the RAN 120A and 120B can be referredto as access nodes (ANs), access points (APs), base stations (BSs), NodeBs, eNodeBs, and so on. For example, an eNodeB (also referred to as anevolved NodeB) is typically a base station that supports wireless accessby UEs 102 according to the LTE wireless interface defined by 3GPP.These access points can be terrestrial access points (or groundstations), or satellite access points.

Both RANs 120A and 120B are configured to connect to a core network 140Aand 140B, respectively, that can perform a variety of functions,including routing and connecting circuit switched (CS) calls between UEs102 served by the RAN 120A/120B and other UEs 102 served by the RAN120A/120B or UEs served by a different RAN altogether, and can alsomediate an exchange of packet-switched (PS) data with external networkssuch as Internet 175 and external clients and servers.

The Internet 175 includes a number of routing agents and processingagents (not shown in FIG. 1 for the sake of convenience). In FIG. 1, UE102-N is shown as connecting to the Internet 175 directly (i.e.,separate from the core networks 140A and 140B, such as over an Ethernetconnection of WiFi or 802.11-based network). The Internet 175 canthereby function to route and connect packet-switched datacommunications between UE 102-N and UEs 102-1 to 102-5 via the corenetwork 140A/140B.

Also shown in FIG. 1 is the access point 125 that is separate from theRANs 120A and 120B. The access point 125 may be connected to theInternet 175 independently of the core networks 140A and 140B (e.g., viaan optical communication system such as FiOS, a cable modem, etc.). Theair interface 108 may serve UE 102-4 or UE 102-5 over a local wirelessconnection, such as IEEE 802.11 in an example. UE 102-N is shown as adesktop computer with a wired connection to the Internet 175, such as adirect connection to a modem or router, which can correspond to theaccess point 125 itself in an example (e.g., for a WiFi router with bothwired and wireless connectivity).

Referring to FIG. 1, location servers 170A and 170B are shown asconnected to the Internet 175, the core networks 140A and 140B,respectively, or both. The location servers 170A and 170B can each beimplemented as a plurality of structurally separate servers, oralternately may each correspond to a single server. As will be describedbelow in more detail, the location servers 170A and 170B are configuredto support one or more location services for UEs 102 that can connect tothe location servers 170A and 170B via the core networks 140A and 140B,respectively, and/or via the Internet 175.

An example of a protocol-specific implementation for the RANs 120A and120B and the core networks 140A and 140B are provided below with respectto FIG. 2 to help explain the wireless communications system 100 in moredetail. In particular, the components of the RANs 120A and 120B and thecore networks 140A and 140B correspond to components associated withsupporting packet-switched (PS) communications, whereby legacycircuit-switched (CS) components may also be present in these networks,but any legacy CS-specific components are not shown explicitly in FIG.2.

FIG. 2 illustrates an example configuration of a portion of the RANs120A and 120B and a portion of the core network 140A based on an LTE orLTE-U network, in accordance with an aspect of the disclosure. Referringto FIG. 2, RAN 120A is configured with a plurality of evolved Node Bs(also referred to as eNodeBs or eNBs) 202, 204 and 206, and RAN 120B isconfigured with a plurality of eNodeBs 208 and 210. The eNodeBs 202 to210 may be configured to broadcast a Positioning Reference Signal (PRS)to nearby UEs 102 to enable any UE 102 to make measurements of PRStiming differences between pairs of eNodeBs. The PRS timing differencemeasurements may enable a location estimate of the UE 102 to beobtained, according to the Observed Time Difference of Arrival (OTDOA)positioning method, either by the UE 102 itself (e.g., if the UE 102 isprovided with location coordinates and timing information for themeasured eNodeBs by a location server) or by a location server (e.g., alocation server 170) to which the PRS timing difference measurements maybe sent. OTDOA is a multilateration method in which the UE 102 measuresthe time difference, known as a Reference Signal Time Difference (RSTD),between specific signals (e.g., PRS signals) from different pairs ofeNodeBs and either reports the RSTD measurements to a location server orcomputes a location itself from the RSTD measurements.

In the example of FIG. 2, eNodeB 202 is shown as a Home eNodeB (HeNB)and interfaces with the RAN 120A via a HeNB gateway 245. The Home eNodeB202 is an example of a “small cell base station.” The term “small cell”generally refers to a class of low-powered access points that mayinclude or be otherwise referred to as femto cells, pico cells, microcells, home base stations, Wi-Fi APs, other small coverage area APs,etc. A small cell may be deployed to supplement macro cell coverageand/or increase network capacity. A small cell may provide wirelesscoverage indoors such as within a house, office, a portion of a largebuilding, a portion of a convention center, shopping mall, etc. A smallcell may instead or in addition provide wireless coverage outdoors suchas over an area covering part of a block or a few blocks within aneighborhood. Small cells may communicate using unlicensed frequencybands, as opposed to macro cells, which may typically communicate usinglicensed frequency bands.

In FIG. 2, the core network 140A includes an Enhanced Serving MobileLocation Center (E-SMLC) 225, a Mobility Management Entity (MME) 215, aGateway Mobile Location Center (GMLC) 220, a Serving Gateway (S-GW) 230,a Packet Data Network Gateway (P-GW) 235, and a Secure User PlaneLocation (SUPL) Location Platform (SLP) 240. Although not illustrated inFIG. 2 for the sake of simplicity, core network 140B may include thesame or similar network entities. In the example of FIG. 2, the locationserver 170A in FIG. 1 may correspond to one or more of the E-SMLC 225,the GMLC 220, or the SLP 240. Additionally, the location server 170B inFIG. 1 may correspond to the SLP 260.

Network interfaces between the components of the core network 140A, theRAN 120A, and the Internet 175 are illustrated in FIG. 2 and are definedin Table 1 (below) as follows:

TABLE 1 LTE Core Network Connection Definitions Network InterfaceDescription S1-MME Reference point for the control plane protocolbetween RAN 120A and MME 215. S1-U Reference point between RAN 120A andS-GW 230 for the per bearer user plane tunneling and inter-eNodeB pathswitching during handover. S5 Provides user plane tunneling and tunnelmanagement between S-GW 230 and P-GW 235. It is used for S-GW relocationdue to UE mobility and if the S-GW 230 needs to connect to anon-collocated P-GW for the required PDN connectivity. S8 Inter-PLMNreference point providing user and control plane between the S-GW 230 ina Visited Public Land Mobile Network (VPLMN) and the P-GW 235 in a HomePublic Land Mobile Network (HPLMN). S8 is the inter-PLMN variant of S5.P-GW 235 is shown as being in the same Public Land Mobile Network (PLMN)as S-GW 230 in FIG. 2 so only the S5 interface may apply in FIG. 2. Butthe S8 interface would apply if P-GW 235 was located in a different PLMN(e.g., Core Network 140B). S11 Reference point between MME 215 and S-GW230. SGi Reference point between the P-GW 235 and a packet data network(PDN), shown in FIG. 2 as the Internet 175. The PDN may be an operatorexternal public or private packet data network or an intra-operatorpacket data network (e.g., for provision of IMS services). Thisreference point corresponds to Gi for 3GPP accesses. X2 Reference pointbetween two different eNodeBs used for UE handoffs.

A high-level description of some of the components shown in the RANs120A and 120B and the core network 140A of FIG. 2 is now provided.However, these components are each well-known in the art from various3GPP and Open Mobile Alliance (OMA) Technical Specifications (TSs), andthe description contained herein is not intended to be an exhaustivedescription of all functionalities performed by these components.

Referring to FIG. 2, the MME 215 is configured to manage the controlplane signaling for the Evolved Packet System (EPS). MME functionsinclude: Non-Access Stratum (NAS) signaling, NAS signaling security,Mobility management for UEs 102 including support for inter-RAN andintra-RAN handovers, P-GW and S-GW selection, and MME selection forhandovers with a change of MME.

The S-GW 230 is the gateway that terminates the interface toward the RAN120A. For each UE 102 attached to the core network 140A for an LTE-basedsystem, at a given point of time, there can be a single S-GW 230. Thefunctions of the S-GW 230 include: serving as a mobility anchor point,packet routing and forwarding, and setting the Differentiated ServicesCode Point (DSCP) based on a Quality of Service (QoS) Class Identifier(QCI) of an associated EPS bearer.

The P-GW 235 is the gateway that terminates the SGi interface toward thePacket Data Network (PDN), e.g., the Internet 175. If a UE 102 isaccessing multiple PDNs, there may be more than one P-GW 235 for that UE102. P-GW 235 functions include: providing PDN connectivity to UEs 102,UE IP address allocation, setting the DSCP based on the QCI of theassociated EPS bearer, accounting for inter operator charging, uplink(UL) and downlink (DL) bearer binding, and UL bearer bindingverification.

As further illustrated in FIG. 2, an external client 250 may beconnected to the core network 140A via the GMLC 220 and/or the SLP 240.The external client 250 may optionally be connected to the core network140A, the core network 140B and/or the SLP 260 via the Internet 175. Theexternal client 250 may be a server, a web server, or a user device,such as a personal computer, a UE, etc.

The HeNB Gateway 245 in FIG. 2 may be used to support connection ofsmall cells and/or HeNBs, such as HeNB 202. HeNB Gateway 245 may includeor be connected to a Security Gateway (not shown in FIG. 2). TheSecurity Gateway may help authenticate the small cells and/or HeNBs,such as HeNB 202, and/or may enable secure communication between thesmall cells and/or HeNBs, such as HeNB 202, and other network entities,such as MME 215. The HeNB Gateway 245 may perform protocol relaying andconversion in order to allow small cells and/or HeNBs, such as HeNB 202,to communicate with other entities, such as MME 215.

The E-SMLC 225 may be a location server that supports a control planelocation solution enabling a location of a UE 102 with LTE or LTE-Uradio access to be obtained. With a control plane (CP) locationsolution, the signaling used to initiate positioning of a UE 102 and thesignaling related to the positioning of the UE 102 can occur overinterfaces of a cellular network and using protocols that supportsignaling (as opposed to data or voice transfer). The functions of theE-SMLC 225 may include: (i) managing a location session to determine alocation of a UE 102; (ii) initiating one or more position methods toobtain location related measurements for a UE 102 (e.g., from the UE 102and/or from eNodeBs 202-206 in RAN 120A); and/or (iii) providingassistance data to a UE 102 to enable the UE 102 to obtain locationrelated measurements and/or determine a location estimate for the UE 102from such location related measurements. The E-SMLC 225 may be accessedby the MME 215, which may transfer a location request for a UE 102received from GMLC 220 to E-SMLC 225 and return any location estimatedetermined by the E-SMLC 225 back to the GMLC 220.

The GMLC 220 may be a location server that enables an external client,such as external 250, to request and obtain a location estimate for a UE102. Functions of the GMLC 220 may include authenticating andauthorizing an external client 250 and requesting and obtaining alocation estimate for a UE 102 from the MME 215 on behalf of theexternal client 250.

The SLP 240 and SLP 260 may support the Secure User Plane Location(SUPL) location solution defined by the OMA, which is a user plane (UP)location solution. With a UP location solution, signaling to initiateand perform positioning of a UE 102 may be transferred using interfacesand protocols that support transfer of data (and possibly voice andother media). With the SUPL UP location solution, the location servermay include or take the form of a SUPL Location Platform (SLP), such asSLP 240 or SLP 260. In FIG. 2, either or both of SLPs 240 and 260 may bea Home SLP (H-SLP) for one or more of UEs 102, an emergency SLP (E-SLP),and/or a Discovered SLP (D-SLP). The functions of the SLPs 240 and 260may include some or all of the functions described previously for boththe E-SMLC 225 and the GMLC 220.

In order to support location of a UE 102, the E-SMLC 225, SLP 240, andSLP 260 may support one or more positioning protocols, such as the LTEPositioning Protocol (LPP) defined by 3GPP or the LPP extensions (LPPe)protocol defined by OMA. A positioning protocol may be used between a UE102 and a location server 170, such as the E-SMLC 225, SLP 240, or SLP260, to coordinate and control position determination for a UE 102. Thepositioning protocol may define: (a) positioning related procedures thatmay be executed by the location server 170 and/or the UE 102; and/or (b)communication or signaling exchanged between the UE 102 and the locationserver 170 related to positioning of the UE 102. For control planelocation, the E-SMLC 225 may use a positioning protocol, such as the LPPA protocol (LPPa) defined by 3GPP, to obtain location relatedinformation for a UE 102 from elements in the RAN 120A, such as any ofeNodeBs 202-206. The location related information that is obtained mayinclude location related measurements for the UE 102 or otherinformation to assist location of the UE 102, such as information on PRSsignals transmitted by one or more of eNodeBs 202-206 or locationcoordinates of one or more of eNodeBs 202-206. LPP is well-known anddescribed in various publicly available technical specifications (TSs)from 3GPP (e.g., 3GPP TS 36.355). LPPe has been defined by the OMA(e.g., in OMA TS OMA-TS-LPPe-Vl_0) and may be used in combination withLPP such that an LPP message may contain an embedded LPPe message in acombined LPP/LPPe message. LPPa is described in 3GPP TS 36.455.

A location estimate (e.g., for a UE 102) may be referred to by othernames, such as a position estimate, location, position, position fix,fix, or the like. A location estimate may be geodetic and comprisecoordinates (e.g., latitude, longitude, and possibly altitude) or may becivic and comprise a street address, postal address, or some otherverbal description of a location. A location estimate may further bedefined relative to some other known location or defined in absoluteterms (e.g., using latitude, longitude, and possibly altitude). Alocation estimate may include an expected error or uncertainty (e.g., byincluding an area or volume within which the location is expected to beincluded with some specified or default level of confidence).

FIG. 3 illustrates several sample components (represented bycorresponding blocks) that may be incorporated into an apparatus 302, anapparatus 304, and an apparatus 306 (corresponding to, for example, aUE, a base station (e.g., an eNodeB), and a network entity or locationserver, respectively) to support the operations as disclosed herein. Asan example, the apparatus 302 may correspond to a UE 102, the apparatus304 may correspond to any of eNodeBs 202-210, and the apparatus 306 maycorrespond to the E-SMLC 225, SLP 240, SLP 260, or GMLC 220. It will beappreciated that the components may be implemented in different types ofapparatuses in different implementations (e.g., in an ASIC, in an SoC,etc.). The illustrated components may also be incorporated into otherapparatuses in a communication system. For example, other apparatuses ina system may include components similar to those described to providesimilar functionality. Also, a given apparatus may contain one or moreof the components. For example, an apparatus may include multipletransceiver components that enable the apparatus to operate on multiplecarriers and/or communicate via different technologies.

The apparatus 302 and the apparatus 304 each include at least onewireless communication device (represented by the communication devices308 and 314) for communicating with other nodes via at least onedesignated radio access technology (RAT) (e.g., LTE). Each communicationdevice 308 includes at least one transmitter (represented by thetransmitter 310) for transmitting and encoding signals (e.g., messages,indications, information, and so on) and at least one receiver(represented by the receiver 312) for receiving and decoding signals(e.g., messages, indications, information, pilots, and so on). Forexample, transmitter 310 may be used to transmit an uplink PRS signal toassist location of the apparatus 302 according to techniques describedherein. Similarly, each communication device 314 includes at least onetransmitter (represented by the transmitter 316) for transmittingsignals (e.g., messages, indications, information, pilots, and so on)and at least one receiver (represented by the receiver 318) forreceiving signals (e.g., messages, indications, information, and so on).

A transmitter and a receiver may comprise an integrated device (e.g.,embodied as a transmitter circuit and a receiver circuit of a singlecommunication device) in some implementations, may comprise a separatetransmitter device and a separate receiver device in someimplementations, or may be embodied in other ways in otherimplementations. A wireless communication device (e.g., one of multiplewireless communication devices) of the apparatus 304 may also comprise aNetwork Listen Module (NLM) or the like for performing variousmeasurements.

The apparatus 304 and the apparatus 306 include at least onecommunication device (represented by the communication device 320 andthe communication device 326) for communicating with other nodes. Forexample, the communication device 326 may comprise a network interfacethat is configured to communicate with one or more network entities viaa wire-based or wireless backhaul connection. In some aspects, thecommunication device 326 may be implemented as a transceiver configuredto support wire-based or wireless signal communication. Thiscommunication may involve, for example, sending and receiving: messages,parameters, or other types of information. Accordingly, in the exampleof FIG. 3, the communication device 326 is shown as comprising atransmitter 328 and a receiver 330. Similarly, the communication device320 may comprise a network interface that is configured to communicatewith one or more network entities via a wire-based or wireless backhaul.As with the communication device 326, the communication device 320 isshown as comprising a transmitter 322 and a receiver 324.

The apparatuses 302, 304, and 306 also include other components that maybe used in conjunction with the operations as disclosed herein. Theapparatus 302 includes a processing system 332 for providingfunctionality relating to, for example, positioning reference signaling(PRS) support and/or propagation time measurement in a licensed orunlicensed frequency band as disclosed herein and for providing otherprocessing functionality. The apparatus 304 includes a processing system334 for providing functionality relating to, for example, PRS supportand/or propagation time measurement in a licensed or unlicensedfrequency band as disclosed herein and for providing other processingfunctionality. The apparatus 306 includes a processing system 336 forproviding functionality relating to, for example, PRS support and/orpropagation time measurement in a licensed or unlicensed frequency bandas disclosed herein and for providing other processing functionality.

The apparatuses 302, 304, and 306 include memory components 338, 340,and 342 (e.g., each including a memory device), respectively, formaintaining information (e.g., information indicative of reservedresources, thresholds, parameters, and so on). In addition, theapparatuses 302, 304, and 306 include user interface devices 344, 346,and 348, respectively, for providing indications (e.g., audible and/orvisual indications) to a user and/or for receiving user input (e.g.,upon user actuation of a sensing device such a keypad, a touch screen, amicrophone, and so on).

For convenience, the apparatuses 302, 304, and/or 306 are shown in FIG.3 as including various components that may be configured according tothe various examples described herein. It will be appreciated, however,that the illustrated blocks may have different functionality indifferent designs.

The components of FIG. 3 may be implemented in various ways. In someimplementations, the components of FIG. 3 may be implemented in one ormore circuits such as, for example, one or more processors and/or one ormore ASICs (which may include one or more processors). Here, eachcircuit may use and/or incorporate at least one memory component forstoring information or executable code used by the circuit to providethis functionality. For example, some or all of the functionalityrepresented by blocks 308, 332, 338, and 344 may be implemented byprocessor and memory component(s) of the apparatus 302 (e.g., byexecution of appropriate code and/or by appropriate configuration ofprocessor components). Similarly, some or all of the functionalityrepresented by blocks 314, 320, 334, 340, and 346 may be implemented byprocessor and memory component(s) of the apparatus 304 (e.g., byexecution of appropriate code and/or by appropriate configuration ofprocessor components). Also, some or all of the functionalityrepresented by blocks 326, 336, 342, and 348 may be implemented byprocessor and memory component(s) of the apparatus 306 (e.g., byexecution of appropriate code and/or by appropriate configuration ofprocessor components).

In an aspect, the apparatus 304 may correspond to a “small cell” or aHome eNodeB, such as Home eNodeB 202 in FIG. 2. The apparatus 302 maytransmit and receive messages via a wireless link 360 with the apparatus304, the messages including information related to various types ofcommunication (e.g., voice, data, multimedia services, associatedcontrol signaling, etc.). The wireless link 360 may operate over acommunication medium of interest, shown by way of example in FIG. 3 asthe medium 362, which may be shared with other communications as well asother RATs. A medium of this type may be composed of one or morefrequency, time, and/or space communication resources (e.g.,encompassing one or more channels across one or more carriers)associated with communication between one or more transmitter/receiverpairs, such as the apparatus 304 and the apparatus 302 for the medium362.

As a particular example, the medium 362 may correspond to at least aportion of an unlicensed frequency band shared with (an)other RAN and/orother APs and UEs. In general, the apparatus 302 and the apparatus 304may operate via the wireless link 360 according to one or more radioaccess types, such as LTE or LTE-U, depending on the network in whichthey are deployed. These networks may include, for example, differentvariants of CDMA networks (e.g., LTE networks), Time Division MultipleAccess (TDMA) networks, Frequency Division Multiple Access (FDMA)networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA(SC-FDMA) networks, and so on. Although different licensed frequencybands have been reserved for wireless communications (e.g., by agovernment entity such as the Federal Communications Commission (FCC) inthe United States), certain communication networks, in particular thoseemploying small cell base stations, have extended operation intounlicensed frequency bands, such as the Unlicensed National InformationInfrastructure (U-NII) band used by Wireless Local Area Network (WLAN)technologies, most notably IEEE 802.11x WLAN technologies generallyreferred to as “Wi-Fi,” and LTE in unlicensed spectrum technologiesgenerally referred to as “LTE-U” or “MuLTEFire.”

Due to the shared use of the communication medium 362, there is thepotential for interference between the wireless link 360 and otherwireless links on the shared medium 362. Further, for unlicensedspectrum, some radio access types and some jurisdictions may requirecontention or “Listen Before Talk (LBT)” for access to the communicationmedium 362. As an example, a Clear Channel Assessment (CCA) protocol maybe used in which each device verifies via medium sensing the absence ofother traffic on a shared communication medium before seizing (and insome cases reserving) the communication medium 362 for its owntransmissions. In some designs, the CCA protocol may include distinctCCA Preamble Detection (CCA-PD) and CCA Energy Detection (CCA-ED)mechanisms for yielding the communication medium to signaling, voice,and data for a UE (e.g., apparatus 302) or base station (e.g., apparatus304). The European Telecommunications Standards Institute (ETSI), forexample, mandates contention for all devices regardless of their radioaccess type on certain communication mediums such as unlicensedfrequency bands.

Apparatus 302 may also include a positioning measurements component 352that may be used to obtain location related measurements of signals(e.g., PRS or other signals) transmitted by a base station or AP (e.g.,any of eNodeBs 202-210) according to techniques described herein.Location related measurements may include measurements of RSTD for OTDOApositioning and/or measurements of signal propagation time or round triptime (RTT) between a UE 102 and a base station or AP, such as any ofeNodeBs 202-210.

Apparatus 304 and 306 may each include a user equipment positioningcomponent 354 and 356, respectively, which may be used to determine alocation estimate for a UE 102 (e.g., apparatus 302), according totechniques described herein, based on location related measurementsprovided by the UE 102 and/or by a base station or AP, such as any ofeNodeBs 202-120. Location related measurements obtained by the UE 102may include measurements of RSTD for OTDOA positioning and/ormeasurements of signal propagation time or RTT between a UE 102 and abase station or AP, such as any of eNodeBs 202-210. Location relatedmeasurements obtained by any of eNodeBs 202-210 (e.g., apparatus 304)may include measurements of signal propagation time or RTT between theUE 102 and a base station or AP, such as any of eNodeBs 202-210.

Methods to position a UE, such as any of the UEs 102 in FIG. 1, includesuch methods as Enhanced Cell ID (ECID), OTDOA, and Uplink TimeDifference of Arrival (UTDOA). With OTDOA, as described previously, a UE102 may measure RSTDs between pairs of eNodeBs (e.g., eNodeBs 202-210)and then either provide the RSTD measurements to a location server(e.g., E-SMLC 225, SLP 240, or SLP 260) for computation of a location ofthe UE 102 or compute the location itself (e.g., based on locationcoordinates for the eNodeBs that may have been provided to the UE 102 bya location server). With ECID, a UE 102 may make measurements of signalsfrom individual eNodeBs (e.g., any of eNodeBs 202-210) such asmeasurements of a Reference Signal Received Power (RSRP), a ReferenceSignal Received Quality (RSRQ), and/or signal propagation time or RTT.As with OTDOA, the UE 102 may then either provide the measurements(e.g., of RSRP, RSRQ, and/or RTT) to a location server (e.g., E-SMLC225, SLP 240, or SLP 260) for computation of a location of the UE 102,or compute the location itself (e.g., based on location coordinates forthe eNodeBs that may have been provided to the UE 102 by a locationserver). With UTDOA, one or more eNodeBs (e.g., one or more of eNodeBs202-210) and/or one more separate location measurement units (LMUs) maymeasure the time of arrival (TOA) of uplink signals transmitted by theUE 102 and may provide the TOA measurements to a location server (e.g.,E-SMLC 225, SLP 240, or SLP 260) for computation of a location of the UE102.

Position methods such as OTDOA and UTDOA are time-based and may requirethe involved eNodeBs to be synchronized within a few nanoseconds or tensof nanoseconds in order to enable accurate measurements (e.g., of RSTDor TOA) that can enable accurate location of a UE 102 (e.g., with anaccuracy of 10-50 meters). There are several main differences betweenperforming positioning operations with LTE wireless access usinglicensed frequency bands (also referred to herein as “LTE” or “LTE inlicensed spectrum”) and unlicensed frequency bands (also referred toherein as “LTE in unlicensed spectrum” or “LTE-U”), from the perspectiveof time-based positioning methods such as OTDOA and UTDOA. For example,with LTE in unlicensed spectrum, while there may be synchronized eNodeBdeployments, synchronization among the eNodeBs may not be supportedbecause synchronization may be difficult and expensive to accuratelyachieve in practice. For example, Home eNodeBs (e.g., Home eNodeB 202)may only be constrained by 3GPP specifications to 0.25 parts per million(ppm) frequency accuracy, whereas macro and local eNodeBs (e.g., eNodeBs204-210) may be constrained to 0.05 and 0.1 ppm frequency accuracy,respectively. A Home eNodeB at the edge of these constraints may driftby 100 nanoseconds (ns) in as little as 400 milliseconds (ms), comparedto a macro eNodeB for which a similar drift would take at least 2seconds and can be more easily corrected.

Another difference is that with LTE in unlicensed spectrum, there may belower interference and a lower likelihood of interference. For example,contention-based medium access is a primary mechanism for accessing theunlicensed environment, which may make it easier for a UE 102 to hearother co-channel eNodeB's pilots (including positioning pilots). Inaddition, eNodeBs operating in an unlicensed environment may moreliberally resort to Channel Selection (for the anchor cell) to operateon a cleaner channel.

In a synchronized environment, being able to use synchronization amongeNodeBs with LTE in unlicensed spectrum may enable use of OTDOApositioning, as described previously. Specifically, a UE 102 may usedownlink time difference of arrival techniques when computing (orassisting a location server in computing) its location. However, unlikewith LTE in licensed spectrum, eNodeBs may not always be able totransmit PRS signals at known predefined times.

As a first solution, an eNodeB operating with LTE-U may use the same PRSopportunities as would be used with LTE, but may only transmit PRSsignals at a predefined PRS opportunity if the eNodeB wins contention ofthe medium for a PRS subframe, and may skip transmitting PRS signals ata predefined PRS opportunity if the eNodeB does not win contention. Asan enhancement, if an eNodeB is aware of another nearby eNodeB with thesame PRS transmission characteristics (e.g., the same predefined PRSsubframes at the same transmission times, the same PRS code, and/or thesame PRS frequency and bandwidth), the eNodeB can free up the sharedmedium (e.g., deterministically or statistically) when the eNodeBexpects PRS transmission from the neighbor eNodeB. The neighbor eNodeBmay do the same, resulting in fewer occasions when both eNodeBs aretransmitting PRS at the same time. Note that while this may appear to besuperficially similar to PRS blanking or PRS muting, it goes beyond PRSblanking and PRS muting in ensuring that the eNodeB can free up themedium for a sufficient amount of time before the PRS opportunity toensure that the neighbor eNodeB captures the medium. As anotherenhancement, to maximize the likelihood of medium acquisition, an eNodeBmay employ shorter or more aggressive contention (e.g., one-shot LBT)for sending PRS signals.

As a second solution, an eNodeB operating according to LTE in unlicensedspectrum can transmit PRS signals in the xth subframe of type Z after aPRS opportunity. For example, the xth subframe of type Z after a PRSopportunity may be the first discovery reference signal (DRS) subframe(which contains the primary synchronization signal (PSS) and enhancedsecondary synchronization signal (eSSS), and thus may require differentPRS mapping). As another example, the xth subframe of type Z after a PRSopportunity may be the first subframe where PRS is allowed according toLTE rules. As yet another example, the xth subframe of type Z after aPRS opportunity may be the first subframe of a frame (in this case thePRS mapping may need to change, depending on the subframe number).

In a third solution, an eNodeB in LTE in unlicensed spectrum cantransmit PRS without performing contention for the medium. This may, insome cases, run afoul of some regional channel access requirements. Asan enhancement, an eNodeB may utilize blanking or muting as in LTE inlicensed spectrum.

For the first and second solutions described above, eNodeBs in LTE inunlicensed spectrum may need to adjust the energy detection (ED) levelfor PRS transmissions. For example, eNodeBs can increase PRSdetectability by employing a lower ED level when contending for PRStransmission. The choice of a lower ED level may be conditional on thePRS-containing transmission opportunity (TxOP) being short (to avoidimpacting capacity), or on the past history of PRS transmissions (e.g.,if PRS opportunities have been skipped for some period of time, the EDlevel can be increased).

FIG. 4A illustrates an example of determining a signal propagation time(e.g., an RTT or a one way propagation time) between an eNodeB 410(which may correspond to any of eNodeBs 202-210) and a UE 102 that useLTE or LTE-U for communication. Referring to FIG. 4A, the eNodeB 410 maytransmit pilot signals during a sequence of downlink subframes 402A andthe UE 102 may transmit pilot signals during a sequence of uplinksubframes 404A. The eNodeB 410 pilot signals may comprise a PRS and/or acell-specific reference signal (CRS), as defined in 3GPP TS 36.211, inone aspect. The UE 102 pilot signals may comprise a PRS in one aspect,where the parameters for the PRS (e.g., PRS code, PRS bandwidth, PRSfrequency, or vshift) are (a) preconfigured in the UE 102, (b) providedto the UE 102 by the eNodeB 410 or a location server (e.g., the E-SMLC225 or SLP 240 or 260), or (c) dependent on (e.g., obtained by the UE102 based on) parameters for the eNodeB 410 (e.g., a physical cell ID orcell global ID for a cell supported by eNodeB 410) or parameters for theUE 102 (e.g., an International Mobile Subscriber Identity (IMSI) orInternational Mobile Equipment Identity (MEM.

As shown in FIG. 4A, the time T_(@eNB) is the time from the beginning ofa downlink LTE subframe at the eNodeB 410 (here, subframe SF_(m)) to thetime a pilot signal indicating the start of the next uplink subframe atthe UE 102 (here, subframe SF_(n)) is received by the eNodeB 410 fromthe UE 102. As also shown in FIG. 4A, the time T_(@UE) is the time fromthe beginning of an uplink subframe at the UE 102 (here, subframeSF_(n+1)) to the time a pilot signal indicating the start of the nextdownlink subframe at the eNodeB 410 (here, subframe SF_(m+1)) isreceived by the UE 102. The time W is the time from the beginning of adownlink subframe at the eNodeB 410 (e.g., subframe SF_(m)) to thebeginning of the immediately following uplink subframe at the UE 102(here, subframe SF_(n)). It may be observed from FIG. 4A that the oneway propagation time between the eNodeB 410 and the UE 102, representedas T_(prop), is given by:

T _(prop) =T _(@eNB) −W  (Equation 1)

T _(prop) =T _(@UE) +W  (Equation 2)

Giving

T _(prop)=(T _(@eNB) +T _(@UE))/2  (Equation 3)

The one way propagation time, T_(prop), is thus half the sum of T_(@eNB)and T_(@UE) and does not depend on the subframe timing difference W.Thus, if the UE 102 measures the time T_(@UE) and the eNodeB 410measures the time T_(@eNB), and the UE 102 and the eNodeB 410 thenprovide the measurements T_(@UE) and T_(@eNB), respectively, to a commonnode, the common node can calculate T_(prop). The common node may be theeNodeB 410 in FIG. 4A, a serving eNodeB for the UE 102 (e.g., if theeNodeB 410 in FIG. 4A is not the serving eNodeB for the UE), the UE 102in FIG. 4A, a location server, such as E-SMLC 225, or some other entity.Using the one way propagation time T_(prop), the RTT may also beobtained as 2*T_(prop).

FIG. 4A shows one particular timing configuration where a subframeboundary occurs at the UE 102 during the propagation of a downlinksignal indicating the start of a new subframe at the eNodeB 410, butwhere a subframe boundary at the eNodeB 410 does not occur during thepropagation of an uplink signal indicating the start of a new subframeat the UE 102. In the case that these conditions are reversed, Equations(1) to (3) above will apply if the roles of the UE 102 and eNodeB 410 inFIG. 4A and in Equations (1) to (3) are reversed. Further, as long asthe propagation time, T_(prop), is less than half the duration of an LTEor LTE-U subframe (which is 1 millisecond) and corresponding to adistance between the UE 102 and eNodeB 410 of less than around 150kilometers, a timing configuration will not occur where a subframeboundary occurs at both the UE 102 and eNodeB 410 during the propagationof a downlink signal indicating the start of a new subframe at theeNodeB 410 and an uplink signal indicating the start of a new subframeat the UE 102, respectively. However, a timing configuration may occurwhere a subframe boundary occurs at neither the UE 102 nor the eNodeB410 during the propagation of a downlink signal indicating the start ofa new subframe at the eNodeB 410 and an uplink signal indicating thestart of a new subframe at the UE 102, respectively. For thisconfiguration, Equation (1) remains as above but Equation 2 would changeto the following:

T _(prop) =T _(@UE) +W−1  Equation 2A)

Giving

T _(prop)=(T _(@eNB) +T _(@UE)−1)/2  Equation 3A)

The common node (e.g., the E-SMLC 225, the UE 102, or the eNodeB 410)that determines the propagation time, T_(prop), may not know whether aconfiguration for Equation (3) or a configuration for Equation (3A)applies. However, provided the propagation time, T_(prop), is less thanhalf the duration of an LTE or LTE-U subframe (i.e., 0.5 ms), the commonnode can compute the propagation time using both Equation (3) andEquation (3A). If a configuration for Equation (3) applies, Equation(3A) will produce a negative result. If a configuration for Equation(3A) applies, Equation (3) will produce a result greater than 0.5 ms.Thus, the equation that does not produce a negative result or a resultgreater than half an LTE or LTE-U subframe (i.e., 0.5 ms) will be thecorrect equation.

FIG. 4B illustrates another example of determining the propagation time(T_(prop)) and/or RTT between the eNodeB 410 and a UE 102. In FIG. 4B,as in FIG. 4A, the eNodeB 410 may transmit pilot signals during asequence of downlink subframes 402B and the UE 102 may transmit pilotsignals during a sequence of uplink subframes 404B. As shown in FIG. 4B,the times T_(@eNB) and T_(@UE) may be the same as described for FIG. 4A,though these times may not be measured. Further, the time X in FIG. 4Bis the time from when a pilot signal indicating the start of an uplinksubframe at the UE 102 (here, subframe SF_(n)) is received by the eNodeB410 and the start of the next downlink subframe at the eNodeB 410 (here,subframe SF_(m+1)). Similarly, the time Y in FIG. 4B is the time fromwhen the UE 102 transmits a pilot signal indicating the start of theuplink subframe at the UE 102 (here, subframe SF_(n)) to the time atwhich the UE 102 receives a pilot signal from the eNodeB 410 indicatingthe start of a downlink subframe at the eNodeB 410 (here, subframeSF_(m+1)). In this case, the propagation delay between the eNodeB 410and the UE 102, represented as T_(prop), is equal to (Y−X)/2. Here, Ycan be measured by the UE 102 and X can be measured by the eNodeB 410.Hence, just as for FIG. 4A, the UE 102 and eNodeB 410 may provide themeasurements Y and X, respectively, to a common node, and the commonnode can calculate T_(prop). As in FIG. 4A, the common node may be theeNodeB 410 in FIG. 4B, a serving eNodeB for the UE 102 (e.g., if theeNodeB 410 in FIG. 4B is not the serving eNodeB for the UE 102), the UE102 in FIG. 4B, a location server, such as the E-SMLC 225, or some otherentity.

For some timing configurations in FIG. 4B, after the UE 102 transmits apilot signal to the eNodeB 410 indicating the start of an uplinksubframe at the UE 102 (e.g., the subframe SF_(n)), the UE 102 mayreceive a pilot signal from the eNodeB 410 indicating the start of adownlink subframe at the eNodeB 410 (e.g., the subframe SF_(m)), whichis not the start of the downlink subframe at the eNodeB 410 (e.g., thesubframe SF_(m+1)) that follows the reception at the eNodeB 410 of thepilot signal indicating the start of the uplink subframe at the UE 102.To measure Y for the correct downlink subframe (e.g., the subframeSF_(m+1)), the UE 102 may wait to receive a pilot signal from the eNodeB410 indicating the start of the next downlink subframe at the eNodeB 410(e.g., the subframe SF_(m+1)). Alternatively, the UE 102 may add theduration of one subframe (which is 1 millisecond for LTE and LTE-U) tothe measurement of Y for the first downlink subframe (e.g., the subframeSF_(m)). Since the UE 102 may not know which is the correct downlinksubframe (e.g., the subframe SF_(m) or the subframe SF_(m+1)) for themeasurement Y, the UE 102 may simply measure Y based on the firstdownlink subframe (e.g., the subframe SF_(m)) and provide themeasurement to the common entity for calculation of T_(prop). As long asT_(prop) is less than half the duration of one LTE or LTE-U subframe(corresponding to the UE 102 and eNodeB 410 being less than about 150kilometers apart), the common entity can determine whether to add onesubframe duration (equal to 1 ms) to the value of Y provided by the UE102 according to whether (Y−X) is or is not negative. If (Y−X) isnegative, the common entity may add one subframe duration to the valueof Y. If (Y−X) is not negative, the common entity may not adjust Y.

Note that other timing measurements and calculations may be used todetermine T_(prop) and/or the RTT between the UE 102 and eNodeB 410shown in FIGS. 4A and 4B, but the concept would remain the same.Further, the downlink pilot signals from the eNodeB 410 that aremeasured by the UE 102 to obtain T_(@UE) (in FIG. 4A) or Y (in FIG. 4B)need not to be the same type of pilot signals sent by the eNodeB 410that are shown in FIGS. 4A and 4B, but may instead be other pilotsignals that have the same properties from the UE 102 perspective butmay be received before or after the downlink pilot signals shown inFIGS. 4A and 4B. The same may apply to the uplink pilot signals from theUE 102 that are measured by the eNodeB 410 to obtain T_(@eNB) (in FIG.4A) or X (in FIG. 4B). However, the time difference between themeasurements by the UE 102 and the eNodeB 410 may need to be limited(e.g., to 100 ms or less) in order to reduce the effects of timing driftat the eNodeB 410 and/or the UE 102, which could otherwise add someerror to the relationship between the UE 102 and the eNodeB 410measurements and the determination of T_(prop) and/or RTT.

As mentioned previously, in FIGS. 4A and 4B, the uplink pilot signalstransmitted by the UE 102 that are measured by the eNodeB 410 and thedownlink pilot signals transmitted by the eNodeB 410 that are measuredby the UE 102 may each be PRS signals. However, the eNodeB 410 may notbe synchronized with other eNodeBs in the same network (e.g., in RAN120A or 120B) and the timing of the eNodeB 410 and the UE 102 in FIGS.4A and 4B may be arbitrary.

A PRS dictionary may define a set of distinct PRS signals that eachdiffer from all other PRS signals in the PRS dictionary due to using adifferent PRS code, different PRS frequency, and/or a different PRStiming. The PRS dictionary for downlink PRS signals may includesufficient PRS signals for the largest number of nodes (e.g., eNodeBs)expected to transmit PRS within the same local geographical area (e.g.,an area within which PRS signals from most or all nodes can be receivedat the same location and/or can cause mutual interference). For uplinkPRS, a large uplink PRS dictionary may enable more UEs (e.g., UEs 102)to transmit PRS signals and take advantage of asynchronous PRS-basedpositioning, as exemplified in association with FIGS. 4A and 4B.

A PRS identity may be a physical cell ID (e.g., with a range of 0 to503) or a PRS ID (e.g., with a range of 0 to 4095) and may be as definedin 3GPP TS 36.211 and TS 36.355 and used to define and generate adistinct PRS code. A location server, such as the E-SMLC 225 or SLP 240or 260, may distribute downlink PRS identities to eNodeBs and/or uplinkPRS identities to UEs 102 and/or eNodeBs. An eNodeB (e.g., any ofeNodeBs 202-210 or eNodeB 410) or a location server (e.g., E-SMLC 225)may provide a PRS identity to a UE 102 and possibly other PRS parameters(e.g., PRS frequency and/or PRS bandwidth) and an indication of when theUE 102 may or should transmit a PRS signal (e.g., a start time, endtime, duration, number of consecutive PRS subframes, and/or periodicityfor PRS transmission by the UE 102). The UE 102 may then transmit thePRS in certain uplink subframes (e.g., as indicated by the eNodeB orlocation server) to enable determination of a propagation time or RTTbetween the UE 102 and one or more other eNodeBs, for example, asdescribed in FIGS. 4A and 4B. The determined propagation time or RTT maybe used (e.g., by a location server) to determine the location of the UE102, for example, using methods already known for the ECID positionmethod or using techniques described later in association with FIG. 5.In some aspects, an uplink PRS transmitted by a UE 102 may be the sameas the PRS defined for eNodeB transmission in 3GPP TS 36.211, buttransmitted uplink and using spectrum allocated for UE transmission. Insome aspects, an uplink PRS transmitted by a UE 102 may be an (enhancedversion of an) uplink physical pilot (e.g., a specific reference signal(SRS)).

An unlicensed environment may offer both benefits (e.g., lowerinterference) and challenges (e.g., PRS signals may not always be ableto win contention of the shared medium) for transmitting PRS signals. Toaddress the contention concern, a sender of a PRS signal (e.g., a UE oreNodeB) may attempt to send PRS signals as part of contention-freesignaling or refrain from sending PRS signals if contention cannot beresolved.

FIG. 5 illustrates an exemplary geographic deployment of various eNodeBs(eNodeBs 202, 204, 206, and 208) and UEs 102 (UEs 102-1, 102-2, 102-3,and 102-4) in the wireless communications system 100 of FIG. 1 and FIG.2. In the example of FIG. 5, eNodeB 204 is the serving eNodeB for UEs102-1 and 102-2 and eNodeB 208 is the serving eNodeB for UE 102-3. Inaddition, eNodeBs 202 and 206 are nearby to UEs 102-1, 102-2, and 102-3(e.g., support neighbor cells for these UEs). For ease of reference inassociation with FIG. 5, UEs 102-1, 102-2, 102-3, and 102-4 are referredto as UE 1, UE 2, UE 3, and UE 4, respectively, and eNodeBs 204, 206,202, and 208 are referred to as eNB 1, eNB 2, eNB 3, and eNB 4,respectively. There may be other eNodeBs and UEs 102 not shown in FIG.5. Further, a UEn (where n is a positive integer) may be referred to asa “UE n” and an eNBm (where m is a positive integer) may be referred toas “eNB m” for clarity in distinguishing the integers n and m when usedas labels for UEs and eNBs.

In order to obtain the locations of one or more of the UEs 102 in FIG.5, a measurement or measurements to enable determination of an RTT or aone-way propagation time between each UE 102 and the UE 102's servingeNodeB may be obtained by each UE 102 and/or by the serving eNodeB foreach UE 102, for example, using the techniques described previously inassociation with FIGS. 4A and 4B. Each UE 102 may also or insteadmeasure one or more RSTDs between pairs of nearby eNodeBs (e.g., whichmay or may not include the serving eNodeB for the UE 102). Themeasurements may then be sent to a location server (or other commonnode), such as the E-SMLC 225 or SLP 240 or 260. The location server maythen determine an RTT or a propagation delay between each UE 102 and theserving eNodeB for the UE 102 (e.g., using the techniques described inassociation with FIGS. 4A and 4B). The location server may then use thedetermined RTTs or propagation times and the RSTD measurements providedby each UE 102 to obtain the location of each UE 102. The locationserver may make use of the known locations of the eNodeBs and any knownreal time differences (RTDs) in the transmission timing between theeNodeBs to compute the UE 102 locations.

In a synchronized network, the RTDs between pairs of eNodeBs may all bezero if the eNodeBs are synchronized to the same time (e.g., if thestart of each new LTE or LTE-U subframe at each eNodeB occurs atprecisely the same time and/or if the start of system frame number zeroat each eNodeB occurs at precisely the same time). In other synchronizednetwork implementations, while LTE or LTE-U timing may not be the samefor all eNodeBs, the RTDs between pairs of eNodeBs may be constant andmay be known from information used to configure the synchronization. Aproblem may occur, however, if the eNodeBs are part of an asynchronousnetwork (e.g., an LTE-U network), since the RTDs between pairs eNodeBsmay typically not be known and/or may not remain constant over longperiods of time (e.g., an hour or more). In that case, the locationserver may use additional RSTD measurements from UEs 102 (if available)to both position the UEs 102 and obtain the RTDs between the eNodeBs byusing the additional RSTD measurements to solve for the additionalunknown RTDs. However, this may not be possible if UEs 102 are only ableto obtain one or a few RSTD measurements, since there may then beinsufficient RSTD measurements to solve for both the unknown UE locationcoordinates and unknown RTDs. In such a case, the location server mayuse both RSTD and RTT measurements to locate UEs 102 and obtain RTDs, asdescribed below.

In the example shown in FIG. 5, RSTDs, RTDs, ranges, and other relatedvariables and parameters are defined as follows:

-   -   TOA_(ij)=Time of Arrival of an uplink signal from eNodeB i at UE        j    -   T_(i)=Transmission time of an uplink signal at eNodeB i    -   RSTD_(ijk)=an RSTD measurement between eNodeBs i and j obtained        by UE k and given by (TOA_(ik)-TOA_(jk)), where the TOAs are        measured for corresponding signals (e.g., signals indicating the        start of a new subframe at each eNodeB)    -   RTD_(ij)=an RTD between eNodeBs (or cells) i and j, given by        (T_(i)-T_(j)) for transmission of corresponding signals (e.g.,        indicating the start of a new subframe at an eNodeB)    -   R_(ij)=a range (e.g., straight line distance) from an antenna        for eNodeB i to UEj        Then for eNodeBs i and k and UEs j and m:

R _(ij) −R _(kj) =c*(RSTD_(ikj)−RTD_(ik))  (Equation 4)

R _(im) −R _(km) =c*(RSTD_(ikm)−RTD_(ik))  (Equation 5)

Where c=signal propagation speed (e.g., the speed of light)

Giving

R _(km) −R _(kj) =c*(RSTD_(ikj)−RSTD_(ikm))+(R _(im) −R_(ij))  (Equation 6)

Equation (6) may be valid for a condition (a) in which the same uplinksignals from the eNodeBs i and k are measured by both UEs j and m toobtain the RSTDs or a condition (b) in which the uplink signals measuredby UE j are transmitted by eNodeBs i and k at the same time interval(e.g., by the same integer number of LTE or LTE-U subframes) before orafter the corresponding uplink signals measured by UE m. To enablecondition (a) or condition (b) in other cases A and B (as describedfurther below), a location server may uniquely adjust one of the RSTDmeasurements for either UE j or UE m by adding or subtracting an integermultiple of the LTE subframe time (1 ms). For case A, the locationserver is assumed not to know the location of UE m or UE j and the RSTDmeasurement is uniquely adjusted to be within one half subframe duration(e.g., 0.5 ms) of the other (unadjusted) RSTD measurement. The RSTDadjustment for case A may ensure condition (a) or (b) when the pair ofeNodeBs i and k are separated from one another by less than one quarterof the signal propagation distance over one LTE or LTE-U subframe (about75 kms). This is because the RSTD for the same signals from the pair ofeNodeBs i and k (and measured by UE m or j at any arbitrary location)may have to lie within a window of duration 2*T, where T is the signalpropagation time between the two eNodeBs i and k. To ensure the twoRSTDs are within 0.5 ms of each other, T should be less than 0.25 ms asassumed for case A. A location server may verify that the adjustment canbe used for case A by verifying that the locations of two eNodeBs i andk are within around 75 km of each other: if the eNodeBs i and k areseparated by more than 75 kms the location server may not be able to useEquation (6). For case B, the location server is assumed to know theapproximate locations of UE m and UE j with enough accuracy to determinean expected difference between the two RSTD measurements to within onehalf the duration of an LTE subframe (i.e., 0.5 ms). For case B, thelocation server may uniquely adjust one RSTD by an integer multiple ofone LTE subframe duration (i.e., 1 ms) so that the difference of the twoRSTDs is within 0.5 ms of the expected difference between the two RSTDs.For case B, the eNodeBs i and k may be separated by any distance (e.g.,a distance greater than 75 kms). The adjustment of one RSTD in Equation(6) as just described may be used in other equations containing twoRSTDs for the same pair of eNodeBs, such as Equation (7) describedfurther below.

In Equation (6), R_(im) and R_(ij) can be known if eNodeB i is theserving eNodeB for UEs m and j and if the RTT or one way propagationtime between eNodeB i and each of UEs m and k is measured or determined,for example, as described previously in association with FIGS. 4A and4B. Additionally, UE j may measure and provide RSTD_(ikj) and UE m maymeasure and provide RSTD_(ikm). In that case, all quantities on theright hand side of Equation (6) can be determined and known, forexample, by a location server. This provides a known value for the lefthand side of Equation (6), which gives the difference between the rangesof UEs m and j to the common eNodeB k. In obtaining this value, the UEsm and j should each measure an RSTD between their common serving eNodeBi and the eNodeB k and assist determination of (or measure) thepropagation time from each UE to the common serving eNodeB i. If theRSTD measurement by UEs m and j is repeated for another eNodeB n,another equation can be obtained in the same way as Equation (6) as:

R _(nm) −R _(nj) =c*(RSTD_(inj)−RSTD_(inm))+(R _(im) −R_(ij))  (Equation 7)

As in the case of Equation (6), all quantities on the right hand side ofEquation (7) can be determined and known, for example, by a locationserver. This provides a known value for the left hand side of Equation(7), which gives the difference between the ranges of UEs m and j to thecommon eNodeB n. In obtaining the left hand sides of both Equations (6)and (7), the UEs m and j need to measure two RSTDs each between theircommon serving eNodeB i and two other common eNodeBs k and n, andmeasurements from the UEs m and j and/or from the common serving eNodeBi are needed to allow determination of the propagation time (or RTT) andhence the range between each UE m and j and the common serving eNodeB i.Using just this information and the known location of each eNodeBantenna for eNodeBs i, k, and n, a location server (e.g., the E-SMLC225) may determine both the locations of the UEs m and j and the RTDsbetween the eNodeBs i, k, and n.

As an example of determining the locations of the UEs m and j, assumethat for the eNodeBs, i=1, k=2, and n=3 and that for the UEs, m=1 andj=2. The UEs and eNodeBs are then as shown in FIG. 5 (e.g., ignoring UE3, UE 4, and eNB 4). Due to knowing R11 and R12 in FIG. 5, UE 1 and UE 2are constrained to lie on the circles 501 and 502 in FIG. 5,respectively, where circle 501 has a radius of R11 and circle 502 has aradius of R12 and both circles are centered on eNB 1. In addition, thedifference between the ranges R21 and R22 of UE 1 and UE 2,respectively, to eNB 2 is known (from Equation (6)) as is the differencebetween the ranges R31 and R32 of UE 1 and UE 2, respectively, to eNB 3(from Equation (7)). These known properties provide four separategeometric constraints on the locations of UE 1 and UE 2 and,equivalently, provide four separate equations for horizontal x and ycoordinates of UE 1 and UE 2 based on Equations (6) and (7) and twoother equations associating the x and y coordinates of UE 1 and UE 2 tothe known circles 501 and 502, respectively. The x and y coordinates ofUE 1 and UE 2 may then be obtained algebraically, for example, byiterative means by starting with approximations for the x and ycoordinates.

Once the locations of UE 1 and UE 2 are obtained, the RTD between theserving eNB 1 and each of eNB 2 and eNB 3 can be obtained using Equation(4) or (5) for eNB 2 and analogs of Equation (4) or (5) for eNB 3. TheRTD between eNB 2 and eNB 3 can then be obtained as the difference ofthe RTDs between eNB 1 and each of eNB 2 and eNB 3. The generalizationof this to any pair of UEs m and j and any three eNodeBs k, and n whereeNodeB i is a common serving eNodeB for UEs m and j is already presentin Equations (4) to (7), though for the purposes of providing theexample in FIG. 5, specific values for i, j, k, m, and n have been used.

The technique as so far described enables location of a pair of UEs 102with a common serving eNodeB that each obtain two RSTD measurementsbetween the common serving eNodeB and two other common eNodeBs and forwhich a range to the common serving eNodeB can be determined frommeasurements of an RTT or propagation time from each UE 102 to thecommon serving eNodeB. However, the technique may be extended to allowlocation of one UE 102 in the pair of UEs 102 some time aftermeasurements are obtained for the other UE 102 in the pair. In addition,the technique may be extended to enable location of other UEs 102 thatobtain RSTD measurements but for which measurements of RTT orpropagation time may not be available and where such location may beobtained at a later time.

As an example of this extension, UE 102-1 in FIG. 5 may measure a firstRSTD between the serving eNodeB 204 and eNodeB 206 and a second RSTDbetween the serving eNodeB 204 and eNodeB 202. The UE 102-1 and/or theserving eNodeB 204 may also make measurements to enable determination ofa first RTT or a first propagation time between UE 102-1 and the servingeNodeB 204 (e.g., as described for FIGS. 4A and 4B). The UE 102-1 mayalso obtain additional RSTD measurements between other pairs of eNodeBs(e.g., between serving eNodeB 204 and eNodeB 208). The measurements maybe sent by UE 102-1 and by serving eNodeB 204, if eNodeB 204 obtains anymeasurements, to a location server (not shown in FIG. 5), such as E-SMLC225. If the UE 102-1 only provides the first and second RSTDmeasurements and no additional RSTD measurements, the location servermay not be able to determine the location of UE 102-1 (e.g., if the RTDsbetween eNodeBs 202, 204, and 206 are unknown). If the UE 102-1 providesthe first and second RSTD measurements and additional RSTD measurements,the location server may be able to determine the location of UE 102-1,by using the additional RSTD measurements to help determine the RTDsbetween eNodeBs 202, 204, and 206. In either case, the location servermay store the received first and second RSTD measurements as well as anyadditional RSTD measurements and the first RTT (or first propagationtime) determined between UE 102-1 and the serving eNodeB 204.

At the same time as measurements are received for UE 102-1 or at somelater time, the location server may receive similar measurements for UE102-2 in FIG. 5. For example, UE 102-2 in FIG. 5 may measure a thirdRSTD between the serving eNodeB 204 and eNodeB 206 and a fourth RSTDbetween the serving eNodeB 204 and eNodeB 202. The UE 102-2 and/or theserving eNodeB 204 may also obtain measurements to enable determinationof a second RTT or second propagation time between UE 102-2 and theserving eNodeB 204. The UE 102-2 may also obtain additional RSTDmeasurements between other pairs of eNodeBs (e.g., between servingeNodeB 204 and eNodeB 208). The measurements may be sent by UE 102-2 andby serving eNodeB 204, if eNodeB 204 obtains any measurements, to thelocation server. If the UE 102-2 only provides the third and fourth RSTDmeasurements and no additional RSTD measurements and if the locationserver is able to determine the second RTT or second propagation time,the location server may employ the technique previously described inassociation with Equations (4) to (7) and FIG. 5 to obtain a locationfor UE 102-2 (as well as a location or previous location for UE 102-1)and RTDs between the eNodeBs 202, 204, and 206. In this case, theprevious technique could use the first and second RSTD measurements andthe first RTT or first propagation time that were stored by the locationserver for UE 102-1 as well as the third and fourth RSTD measurementsand the second RTT or second propagation time determined for UE 102-2.Any additional RSTD measurements provided by UE 102-2 may also be used.As described previously, the technique described in association withEquations (4) to (7) also enables determination of the RTDs betweeneNodeBs 202, 204, and 206. The location server may then store thedetermined RTDs.

At some later time, the location of another UE, e.g., UE 102-3 in FIG.5, may be needed. In this case, UE 102-3 may measure a fifth RSTDbetween eNodeBs 204 and 206 and a sixth RSTD between eNodeBs 204 and202. The UE 102-3 and/or the serving eNodeB 208 for UE 102-3 may alsoobtain measurements to enable determination of a third RTT or thirdpropagation time between UE 102-3 and the serving eNodeB 208. The UE102-3 may also obtain additional RSTD measurements between other pairsof eNodeBs (e.g., between serving eNodeB 208 and one more othereNodeBs). The measurements may be sent by UE 102-3 and by serving eNodeB208, if eNodeB 208 obtains any measurements, to the location server.Since the location server has previously obtained and stored the RTDbetween eNodeBs 204 and 206 and the RTD between eNodeBs 204 and 202, thelocation server may use the fifth and sixth RSTDs to obtain a difference(R13−R23) in the range of UE 102-3 to eNodeBs 204 and 206 (e.g., usingthe fifth RSTD, the RTD between eNodeBs 204 and 206 and Equation (4) or(5)) and a difference (R13−R33) in the range of UE 102-3 to eNodeBs 204and 202 (e.g., using the sixth RSTD, the RTD between eNodeBs 204 and 202and Equation (4) or (5)). If the location server has also determined thethird RTT or third propagation time, the location server can locate theUE 102-3 on the circle 503 in FIG. 5 centered on the serving eNodeB 208and with known radius R43 (equal to the range corresponding to the thirdRTT or propagation time). The two differences in ranges and the locationof UE 102-3 on the circle 503 can be used by the location server toobtain the location of the UE 102-3. If the location server does notreceive measurements (from the UE 102-3 and/or the serving eNodeB 208)enabling determination of the third RTT or third propagation time, thelocation server may still be able to locate UE 102-3 if UE 102-3provides additional RSTD measurements. For example, if UE 102-3 providesan additional RSTD for serving eNodeB 208 and eNodeB 204 and if thelocation server has previously obtained and stored the RTD betweeneNodeBs 204 and 208 (e.g., due to performing the procedure describedpreviously for UEs 102-1 and 102-2 for other UEs or for additional RSTDmeasurements from UEs 102-1 and 102-2 for eNodeBs 204 and 208), thelocation server can locate UE 102-3 using well known principles forOTDOA.

The procedure described above to locate UE 102-3 may be reused to locateother UEs, such as UE 102-4 in FIG. 5, if these other UEs obtain RSTDmeasurements between pairs of eNodeBs and provide these to the locationserver. In this case, RTD or propagation times may also be obtained forsome of these other UEs to assist with location determination (e.g., asdescribed previously for UEs 102-2 and 102-3) or may not be.

The determination of UE 102 locations as described above enables UElocations to be obtained at different times by the location server butmay rely on the determined RTD values remaining almost constant. Toallow for RTDs that may change (e.g., due to timing drift by one or botheNodeBs for each RTD), the location server may obtain new RTD values(e.g., as described above in association with Equations (4) to (7)) whenand as the location of each UE 102 is obtained. The new value for anyRTD may be combined with any existing value for the RTD, for example,using weighted averaging. This may enable more accurate values for RTDsto be obtained and may allow the location server to adjust RTD values instep with actual changes in RTD between pairs of eNodeBs.

The number of RTDs that may need to be stored by the location server fora network comprising N eNodeBs could be approximately N*(M−1)/2 where M(M≤N) is the maximum number of eNodeBs visible to a UE 102 at anylocation such that an RSTD measurement for each eNodeB is possible.However, a location server may store RTDs in a more compact manner toreduce the number of stored RTDs. As an example, the location server maystore a single RTD for each eNodeB using a single reference eNodeB thatis common to all RTDs. Alternatively, a single RTD may be stored foreach eNodeB using a fictitious eNodeB that is common to all RTDs andwhose time corresponds to some precise absolute time (e.g., CoordinatedUniversal Time (UTC time) or Global Positioning System (GPS) time),which may be equivalent to storing the difference in the transmissiontiming of each eNodeB and an absolute time. A location server may alsostore a timestamp for each RTD indicating the most recent time at whichan RTD was obtained or updated. The timestamp may be used by thelocation server to identify RTDs that were obtained or updated at morethan some threshold duration in the past and that may now be inaccuratedue to timing drift in the associated eNodeBs. A location server mayalso maintain statistics (e.g., a standard deviation and/or average rateof increase or decrease) for each RTD (e.g., as determined by comparinga previous value for the RTD with a later value) that may be used by thelocation server to determine a threshold period of time for the RTDduring which the RTD may be expected to remain accurate (e.g., with anexpected change of less than 100 ns).

FIG. 6 illustrates an exemplary flow 600 for determining a distance (orrange) between a first wireless entity 602 and a second wireless entity(not shown) according to at least one aspect of the disclosure. Thefirst wireless entity 602 may be a UE (e.g., any of UEs 102-1 to 102-5or apparatus 302) or a base station, such as an eNodeB (e.g., any ofeNodeBs 202 to 210, apparatus 304, or eNodeB 410) and the secondwireless entity may be the other of the UE or the base station (such asan eNodeB). The base station, whether the first wireless entity 602 orthe second wireless entity, may be the serving base station (such as aserving eNodeB or Home eNodeB) for the UE.

At block 604, the first wireless entity 602 transmits a first PRS signalto the second wireless entity at a first time, and the first PRS signalis received by the second wireless entity at a second time. Means forperforming the functionality associated with block 604 may include, forexample, a communication device, such as communication device 308 or 314in FIG. 3, a processing system, such as processing system 332 or 334 inFIG. 3, or a processing system in conjunction with a communicationdevice, such as processing system 332 or 334 in conjunction withcommunication device 308 or 314, respectively.

At block 606, the first wireless entity 602 receives a second PRS signalfrom the second wireless entity at a third time, where the second PRSsignal was transmitted by the second wireless entity at a fourth time.In an aspect, the first time may occur before the third time. For thisaspect, the first and third PRS signals may be as shown and describedpreviously for FIGS. 4A and 4B, when the first wireless entity 602 isthe UE. If the first wireless entity 602 is the eNodeB, the first andthird PRS signals may be as shown and described previously for FIGS. 4Aand 4B when the eNodeB and the UE roles in FIGS. 4A and 4B are reversed.In another aspect, the first time may occur after the third time. Inthis other aspect, the first and third PRS signals may be as shown anddescribed previously for FIGS. 4A and 4B when the first wireless entity602 is the eNodeB. If the first wireless entity 602 is the UE for thisother aspect, the first and third PRS signals may be as shown anddescribed previously for FIGS. 4A and 4B when the eNodeB and the UEroles in FIGS. 4A and 4B are reversed. Means for performing thefunctionality associated with block 606 may include, for example, acommunication device, such as communication device 308 or 314 in FIG. 3,a processing system, such as processing system 332 or 334 in FIG. 3, ora processing system in conjunction with a communication device, such asprocessing system 332 or 334 in conjunction with communication device308 or 314, respectively.

In an aspect, the first wireless entity 602 and the second wirelessentity may communicate with each other on an unlicensed radio frequencyspectrum, such as LTE in unlicensed spectrum (e.g., LTE-U). In thatcase, the first wireless entity 602 may transmit the first PRS signalafter winning contention of a shared wireless communications mediumbeing utilized for the unlicensed radio frequency spectrum. In anaspect, the first time and the fourth time may each correspond to thestart of a subframe for LTE or LTE-U, as illustrated in FIGS. 4A and 4B.

At block 608, the first wireless entity 602 enables the distance (orrange) to be determined by a location computing entity based on thefirst time, the second time, the third time, and the fourth time. In anaspect, the location computing entity may be the first wireless entity,the second wireless entity, or a location server (not shown), such asthe E-SMLC 225, the SLP 240, or the SLP 260. In one aspect, enabling thedistance to be determined by the location computing entity includessending the first time and the third time to the location computingentity (e.g., using the LPP or LPP/LPPe positioning protocol when thelocation computing entity is a location server, or using the RadioResource Control (RRC) protocol defined by 3GPP for LTE when thelocation computing entity is the second wireless entity). In thisaspect, the location computing entity can determine the distance betweenthe first wireless entity 602 and the second wireless entity (e.g.,using one of the techniques described in association with FIGS. 4A and4B).

In another aspect, the first wireless entity 602 may obtain thedifference between the first time and the third time and sends thedifference to the location computing entity (e.g., using the LPP orLPP/LPPe positioning protocol or the RRC protocol), and the locationcomputing entity can then determine the distance between the firstwireless entity 602 and the second wireless entity (e.g., using thetechnique described in association with FIG. 4B). The difference maycorrespond to the time Y in FIG. 4B when the first wireless entity 602is the UE and the time X in FIG. 4B when the first wireless entity 602is the eNodeB.

In a further aspect, the first time may correspond to the start of anLTE or LTE-U subframe transmitted by the first wireless entity 602 andthe first wireless entity 602 may obtain the difference between thethird time and the start of the current subframe being transmitted bythe first wireless entity 602 and may send the difference to thelocation computing entity (e.g., using the LPP or LPP/LPPe positioningprotocol or the RRC protocol), and the location computing entity canthen determine the distance between the first wireless entity 602 andthe second wireless entity (e.g., using the technique described inassociation with FIG. 4A). In this further aspect, the difference maycorrespond to the time T_(@UE) in FIG. 4A when the first wireless entity602 is the UE and the time T_(@eNB) in FIG. 4A when the first wirelessentity 602 is the eNodeB.

In another aspect of block 608, the first wireless entity 602 enablingthe distance to be determined by the location computing entity may meanthat the first wireless entity 602 is the location computing entity andcalculates the distance itself. Means for performing the functionalityassociated with block 608 may include, for example, a communicationdevice, such as communication device 308 or 314 in FIG. 3, a processingsystem, such as processing system 332 or 334 in FIG. 3, or a processingsystem in conjunction with a communication device, such as processingsystem 332 or 334 in conjunction with communication device 308 or 314,respectively.

In another aspect of the present disclosure, a cooperative positioningmethod is disclosed that can be utilized in an asynchronous unlicensedenvironment. For example, if two UEs (e.g., UEs 102) participate inpositioning operations at roughly the same time and measure an RTT or aone way propagation time between each UE and a common serving eNodeB andan OTDOA RSTD between each of two other common eNodeBs and the commonserving eNodeB, then the positions of both UEs can be computed at acommon node (e.g., the E-SMLC 225) from these measurements and knowledgeof the positions of the involved eNodeBs. There is no synchronicityassumption needed between the eNodeBs.

FIG. 7 illustrates an exemplary flow 700 for cooperatively positioning aUE 102 according to at least one aspect of the disclosure. The flow 700may be performed by the apparatus 306, which may be a location server,such as the location server 170A, the location server 170B, the E-SMLC225, the GMLC 220, the SLP 240, or the SLP 260.

At block 702, the apparatus 306 receives a first propagation timemeasurement and a first plurality of OTDOA RSTD measurements from afirst UE 102 at a first time. The propagation time measurement may be ameasurement of either the RTT or the one way signal propagation timebetween the first UE 102 and a base station (e.g., a serving eNodeB forthe first UE 102). In another aspect, the first propagation timemeasurement may be a measurement that enables determination of an RTT orone way signal propagation time between the first UE 102 and a basestation by apparatus 306, for example, based on another measurementprovided to apparatus 306 by the base station and using the techniquesdescribed in association with FIG. 4A or FIG. 4B. As an example of thisother aspect, the first UE 102 may measure and provide to the apparatus306 a value for either the time Y in FIG. 4B or the time T_(@UE) in FIG.4A and the base station may measure and provide to the apparatus 306either the time X in FIG. 4B or the time T_(@eNB) in FIG. 4A,respectively. Means for performing the functionality associated withblock 702 may include, for example, a communication device, such ascommunication device 326 in FIG. 3, a processing system, such asprocessing system 336 in FIG. 3, or a processing system in conjunctionwith a communication device, such as processing system 336 inconjunction with communication device 326.

At block 704, the apparatus 306 receives a second propagation timemeasurement and a second plurality of OTDOA RSTD measurements from asecond UE 102 at a second time, where the first propagation timemeasurement and the second propagation time measurement are for the samebase station (e.g., the same eNodeB). In an aspect, the firstpropagation time measurement and the second propagation time measurementare for a common serving base station for the first UE 102 and thesecond UE 102. In an aspect, the first and second UEs 102 may be thesame UE. For example, in this aspect, the first propagation timemeasurement and the first plurality of OTDOA RSTD measurements may beobtained by the UE 102 at a different time and at a different locationto the second propagation time measurement and second plurality of OTDOARSTD measurements. This may enable the apparatus 306 to treat the firstpropagation time measurement and the first plurality of OTDOA RSTDmeasurements as if they were obtained by a different UE 102 to thesecond propagation time measurement and the second plurality of OTDOARSTD measurements.

In an aspect, the first time and the second time may be within athreshold period of time of each other. The threshold may be a fewseconds, one minute or up to several hours or more, depending on thetiming accuracy (e.g., clock accuracy) of the base stations. In anaspect, the base stations associated with the first and secondpropagation time measurements and the first and second pluralities ofOTDOA RSTD measurements are not synchronized with each other and/or notsynchronized with some absolute time, such as GPS time or UTC time. Inan aspect, the first and second propagation time measurements and thefirst and second pluralities of OTDOA RSTD measurements may bemeasurements for LTE radio access in unlicensed spectrum (e.g., LTE-U).Means for performing the functionality associated with block 704 mayinclude, for example, a communication device, such as communicationdevice 326 in FIG. 3, a processing system, such as processing system 336in FIG. 3, or a processing system in conjunction with a communicationdevice, such as processing system 336 in conjunction with communicationdevice 326.

At block 706, the apparatus 306 determines at least one real-timedifference between a pair of base stations based on the firstpropagation time measurement, the second propagation time measurement,the first plurality of OTDOA RSTD measurements, and the second pluralityof OTDOA RSTD measurements. The pair of base stations may be associatedwith the first plurality of OTDOA RSTD measurements and the secondplurality of OTDOA RSTD measurements. Means for performing thefunctionality associated with block 706 may include, for example, aprocessing system, such as processing system 336 in FIG. 3.

At block 708, the apparatus 306 receives a third plurality of OTDOA RSTDmeasurements from a third UE 102 at a third time. In an aspect, thesecond time and the third time may be within a threshold period of timeof each other. As before, the threshold may be a few seconds, oneminute, or up to several hours or more, depending on the timing accuracy(e.g., clock accuracy) of the base stations. In an aspect, the secondand third UEs 102 may be the same UE 102. In this aspect, the first andsecond propagation time measurements and the first and secondpluralities of OTDOA RSTD measurements may be previous propagation timemeasurements and previous OTDOA RSTD measurements performed by the sameUE 102. Means for performing the functionality associated with block 708may include, for example, a communication device, such as communicationdevice 326 in FIG. 3, a processing system, such as processing system 336in FIG. 3, or a processing system in conjunction with a communicationdevice, such as processing system 336 in conjunction with communicationdevice 326.

At block 710, the apparatus 306 determines a position of the third UE102 based at least in part on the at least one real-time differencebetween the pair of base stations. In one aspect, the apparatus 306receives (i) the first propagation time measurement and the firstplurality of OTDOA RSTD measurements from the first UE 102, (ii) thesecond propagation time measurement and the second plurality of OTDOARSTD measurements from the second UE 102, and/or (iii) the thirdplurality of OTDOA RSTD measurements from the third UE 102 using the LPPor LPP/LPPe positioning protocol. Means for performing the functionalityassociated with block 710 may include, for example, a processing system,such as processing system 336 in FIG. 3.

The techniques described in association with FIG. 5 provide an exampleof the exemplary flow 700. For example, the first UE 102 may be the UE102-1, the second UE 102 may be the UE 102-2 and the third UE 102 may bethe UE 102-3 in FIG. 5. The same base station in blocks 702 and 704 maybe the serving eNodeB 204 for UEs 102-1 and 102-2 in FIG. 5. The firstplurality of RSTD measurements and the second plurality of RSTDmeasurements in blocks 702 and 704 may each comprise or include RSTDmeasurements for the serving eNodeB 204 and two other common eNodeBs 202and 206 in FIG. 5. For example, the first plurality of RSTD measurementsmay comprise or include the first and second RSTDs described previouslyfor FIG. 5 and the second plurality of RSTD measurements may comprise orinclude the third and fourth RSTDs described previously for FIG. 5. Theapparatus 306 may employ the techniques described previously inassociation with Equations (4) to (7) to determine the at least one RTDat block 706. The at least one RTD determined at block 706 may be an RTDfor eNodeBs 204 and 206, eNodeBs 204 and 202, or eNodeBs 202 and 206 inFIG. 5. The third plurality of RSTD measurements received at block 708may comprise or include the fifth and sixth RSTDs described previouslyfor FIG. 5. Determination of the position of the third UE 102 at block708 may be as described for determination of the position of UE 102-3 inassociation with FIG. 5.

There are a number of benefits to the positioning methods describedherein, such as in LTE in unlicensed spectrum deployment scenarios. Forexample, in 4G and 5G, there is a need for more data to more devices inmore places. Thus, there is a strong need to leverage all spectrum typesto meet data demands and Internet of Things (IoT) challenges. Forexample, in-building enterprises, small businesses, residentialneighborhood, and venues such as indoor stadiums, airports, warehouses,etc. are some of the common deployment areas for LTE in unlicensedspectrum. Thus, LTE in unlicensed spectrum will probably play animportant role for creating private and public 4G (and 5G) networks allaround the world.

There are also a number of beneficial use cases for positioning in LTEin unlicensed spectrum. LTE in unlicensed spectrum is expected to bewidely deployed in public and home scenarios for the upcoming 5Gtechnology. Positioning has become an important need for many mobileapplications. It is expected that there will be a large number of userswith Internet connectivity via LTE in unlicensed spectrum in indoorscenarios where GPS is not accurate and OTDOA is a much bettertechnology for position determination. Thus, the techniques for positiondetermination described herein could be highly beneficial for suchusers.

As another use case, large warehouses are mostly indoor facilities, andas the world moves towards greater connectivity, these warehouses willlikely become connected warehouses. LTE in unlicensed spectrum may bewidely used to provide connectivity in such scenarios. In addition,drones will be used for automatic movement and navigation of items inthese warehouses, thereby further increasing the benefits and use of thetechniques described above.

FIG. 8 illustrates an example first wireless entity apparatus 800represented as a series of interrelated functional modules connected bya common bus 808. A module for transmitting 802 may correspond at leastin some aspects to, for example, a communication device, such ascommunication device 308 or 314 in FIG. 3, and/or a processing system,such as processing system 332 or 334 in FIG. 3, as discussed herein. Amodule for receiving 804 may correspond at least in some aspects to, forexample, a communication device, such as communication device 308 or 314in FIG. 3, and/or a processing system, such as processing system 332 or334 in FIG. 3, as discussed herein. A module for enabling 806 maycorrespond at least in some aspects to, for example, a processingsystem, such as processing system 332 or 334 in FIG. 3, and/or acommunication device, such as communication device 308 or 314 in FIG. 3,as discussed herein.

FIG. 9 illustrates an example location server apparatus 900 representedas a series of interrelated functional modules connected by a common bus912. A module for receiving 902 may correspond at least in some aspectsto, for example, a communication device, such as communication device326 in FIG. 3, and/or a processing system, such as processing system 336in FIG. 3, as discussed herein. A module for receiving 904 maycorrespond at least in some aspects to, for example, a communicationdevice, such as communication device 326 in FIG. 3, and/or a processingsystem, such as processing system 336 in FIG. 3, as discussed herein. Amodule for determining 906 may correspond at least in some aspects to,for example, a processing system, such as processing system 336 in FIG.3, as discussed herein. A module for receiving 908 may correspond atleast in some aspects to, for example, a communication device, such ascommunication device 326 in FIG. 3, and/or a processing system, such asprocessing system 336 in FIG. 3, as discussed herein. A module fordetermining 910 may correspond at least in some aspects to, for example,a communication device, such as communication device 326 in FIG. 3,and/or a processing system, such as processing system 336 in FIG. 3, asdiscussed herein.

The functionality of the modules of FIGS. 8-9 may be implemented invarious ways consistent with the teachings herein. In some designs, thefunctionality of these modules may be implemented as one or moreelectrical components. In some designs, the functionality of theseblocks may be implemented as a processing system including one or moreprocessor components. In some designs, the functionality of thesemodules may be implemented using, for example, at least a portion of oneor more integrated circuits (e.g., an ASIC). As discussed herein, anintegrated circuit may include a processor, software, other relatedcomponents, or some combination thereof. Thus, the functionality ofdifferent modules may be implemented, for example, as different subsetsof an integrated circuit, as different subsets of a set of softwaremodules, or a combination thereof. Also, it will be appreciated that agiven subset (e.g., of an integrated circuit and/or of a set of softwaremodules) may provide at least a portion of the functionality for morethan one module.

In addition, the components and functions represented by FIGS. 8-9, aswell as other components and functions described herein, may beimplemented using any suitable means. Such means also may beimplemented, at least in part, using corresponding structure as taughtherein. For example, the components described above in conjunction withthe “module for” components of FIGS. 8-9 also may correspond tosimilarly designated “means for” functionality. Thus, in some aspectsone or more of such means may be implemented using one or more ofprocessor components, integrated circuits, or other suitable structureas taught herein.

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the aspects disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the aspects disclosed herein may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The methods, sequences and/or algorithms described in connection withthe aspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in random access memory (RAM), flashmemory, read-only memory (ROM), erasable programmable ROM (EPROM),electrically erasable programmable ROM (EEPROM), registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthat the processor can read information from, and write information to,the storage medium. In the alternative, the storage medium may beintegral to the processor. The processor and the storage medium mayreside in an ASIC. The ASIC may reside in a user terminal (e.g., UE). Inthe alternative, the processor and the storage medium may reside asdiscrete components in a user terminal.

In one or more exemplary aspects, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

While the foregoing disclosure shows illustrative aspects of thedisclosure, it should be noted that various changes and modificationscould be made herein without departing from the scope of the disclosureas defined by the appended claims. The functions, steps and/or actionsof the method claims in accordance with the aspects of the disclosuredescribed herein need not be performed in any particular order.Furthermore, although elements of the disclosure may be described orclaimed in the singular, the plural is contemplated unless limitation tothe singular is explicitly stated.

What is claimed is:
 1. A method at a user equipment (UE) for determininga distance from the UE to a base station, comprising: transmitting afirst positioning reference signaling (PRS) signal to the base stationat a first time, wherein the first PRS signal is received by the basestation at a second time, and wherein the first time corresponds to thestart of a first subframe of a cellular radio access technology (RAT)utilizing unlicensed radio frequency spectrum; receiving a second PRSsignal from the base station at a third time, wherein the second PRSsignal is transmitted by the base station at a fourth time, and whereinthe fourth time corresponds to the start of a second subframe of thecellular RAT; and enabling the distance to be determined based on thefirst time, the second time, the third time, and the fourth time.
 2. Themethod of claim 1, wherein the UE transmits the first PRS signal afterwinning contention of a shared wireless communications medium beingutilized for the unlicensed radio frequency spectrum.
 3. The method ofclaim 1, wherein the first time occurs before the third time.
 4. Themethod of claim 1, wherein the first time occurs after the third time.5. The method of claim 1, wherein the UE determines the distance fromthe UE to the base station.
 6. The method of claim 1, wherein the basestation determines the distance from the UE to the base station.
 7. Themethod of claim 1, wherein a location server determines the distancefrom the UE to the base station.
 8. The method of claim 7, whereinenabling the distance to be determined comprises sending the first timeand the third time to the location server.
 9. The method of claim 1,wherein a difference between the first time and the second time is lessthan half a duration of one subframe, and wherein a duration of onesubframe is added to a difference between the first time and the thirdtime based on a value of the difference between the first time and thethird time minus a difference between the second time and the fourthtime being negative.
 10. The method of claim 1, wherein: the firstsubframe comprises one of a plurality of uplink subframes used by the UEfor uplink communications to the base station and the second subframecomprises one of a plurality of downlink subframes used by the basestation for downlink communications to the UE, and the plurality ofuplink subframes and the plurality of downlink subframe are notsynchronized with each other.
 11. An apparatus for determining adistance from a user equipment (UE) to a base station, comprising: atransceiver of the UE configured to: transmit a first positioningreference signaling (PRS) signal to the base station at a first time,wherein the first PRS signal is received by the base station at a secondtime, and wherein the first time corresponds to the start of a firstsubframe of a cellular radio access technology (RAT) utilizingunlicensed radio frequency spectrum; and receive a second PRS signalfrom the base station at a third time, wherein the second PRS signal istransmitted by the base station at a fourth time, and wherein the fourthtime corresponds to the start of a second subframe of the cellular RAT;and at least one processor of the UE configured to: enable the distanceto be determined based on the first time, the second time, the thirdtime, and the fourth time.
 12. The apparatus of claim 11, wherein thetransceiver transmits the first PRS signal after winning contention of ashared wireless communications medium being utilized for the unlicensedradio frequency spectrum.
 13. The apparatus of claim 11, wherein thefirst time occurs before the third time.
 14. The apparatus of claim 11,wherein the first time occurs after the third time.
 15. The apparatus ofclaim 11, wherein the UE determines the distance from the UE to the basestation.
 16. The apparatus of claim 11, wherein the base stationdetermines the distance from the UE to the base station.
 17. The methodof claim 11, wherein a location server determines the distance from theUE to the base station.
 18. The method of claim 17, wherein the at leastone processor being configured to enable the distance to be determinedcomprises the at least one processor being configured to cause thetransceiver to send the first time and the third time to the locationserver.
 19. The method of claim 11, wherein a difference between thefirst time and the second time is less than half a duration of onesubframe, and wherein a duration of one subframe is added to adifference between the first time and the third time based on a value ofthe difference between the first time and the third time minus adifference between the second time and the fourth time being negative.20. The method of claim 11, wherein: the first subframe comprises one ofa plurality of uplink subframes used by the UE for uplink communicationsto the base station and the second subframe comprises one of a pluralityof downlink subframes used by the base station for downlinkcommunications to the UE, and the plurality of uplink subframes and theplurality of downlink subframe are not synchronized with each other. 21.A non-transitory computer-readable medium storing computer-executableinstructions for determining a distance from a user equipment (UE) to abase station, the computer-executable instructions comprising: at leastone instruction instructing the UE to transmit a first positioningreference signaling (PRS) signal to the base station at a first time,wherein the first PRS signal is received by the base station at a secondtime, and wherein the first time corresponds to the start of a firstsubframe of a cellular radio access technology (RAT) utilizingunlicensed radio frequency spectrum; at least one instructioninstructing the UE to receive a second PRS signal from the base stationat a third time, wherein the second PRS signal is transmitted by thebase station at a fourth time, and wherein the fourth time correspondsto the start of a second subframe of the cellular RAT; and at least oneinstruction instructing the UE to enable the distance to be determinedbased on the first time, the second time, the third time, and the fourthtime.
 22. The non-transitory computer-readable medium of claim 21,wherein the UE transmits the first PRS signal after winning contentionof a shared wireless communications medium being utilized for theunlicensed radio frequency spectrum.
 23. The non-transitorycomputer-readable medium of claim 21, wherein the first time occursbefore the third time.
 24. The non-transitory computer-readable mediumof claim 21, wherein the first time occurs after the third time.
 25. Thenon-transitory computer-readable medium of claim 21, wherein adifference between the first time and the second time is less than halfa duration of one subframe, and wherein a duration of one subframe isadded to a difference between the first time and the third time based ona value of the difference between the first time and the third timeminus a difference between the second time and the fourth time beingnegative.
 26. The non-transitory computer-readable medium of claim 21,wherein: the first subframe comprises one of a plurality of uplinksubframes used by the UE for uplink communications to the base stationand the second subframe comprises one of a plurality of downlinksubframes used by the base station for downlink communications to theUE, and the plurality of uplink subframes and the plurality of downlinksubframe are not synchronized with each other.
 27. An apparatus fordetermining a distance from a user equipment (UE) to a base station,comprising: a communication means of the UE configured to: transmit afirst positioning reference signaling (PRS) signal to the base stationat a first time, wherein the first PRS signal is received by the basestation at a second time, and wherein the first time corresponds to thestart of a first subframe of a cellular radio access technology (RAT)utilizing unlicensed radio frequency spectrum; and receive a second PRSsignal from the base station at a third time, wherein the second PRSsignal is transmitted by the base station at a fourth time, and whereinthe fourth time corresponds to the start of a second subframe of thecellular RAT; and a processing means of the UE configured to: enable thedistance to be determined based on the first time, the second time, thethird time, and the fourth time.
 28. The apparatus of claim 27, whereinthe communication means transmits the first PRS signal after winningcontention of a shared wireless communications medium being utilized forthe unlicensed radio frequency spectrum.
 29. The apparatus of claim 27,wherein the first time occurs before the third time.
 30. The apparatusof claim 27, wherein the first time occurs after the third time.